Method for preconditioning polypropylene fabrics for ironing



United States Patent "ice 3,468,044 METHOD FOR PRECONDITIONING POLYPROPYL- ENE FABRICS FOR IRONING George Lopatin and Carl W. Schroeder, Orinda, Califi, assignors to Shell Oil Company, New York, N.Y., a corporation of New York No Drawing. Filed Nov. 26, 1965, Ser. No. 510,026 Int. Cl. D06f 73/00 US. Cl. 38144 4 Claims ABSTRACT OF THE DISCLOSURE The ironing temperature at which polypropylene-containing fabrics can be ironed without becoming hard and shiny is increased by giving the fabric a preliminary heat treatment at a temperature at which the fabric becomes crinkled but below that at which the untreated fabric becomes hard and shiny.

This invention relates to a process for improving the ironability of polypropylene containing fabrics.

Polypropylene and especially highly crystalline polypropylene prepared under low pressure conditions with Ziegler-Natta type catalysts, has become increasingly important in the preparation of fabrics, yard goods, etc., due to the desirable properties of the polymer and the resulting properties of the fabrics prepared therefrom. More specifically, polypropylene containing fabrics have outstanding wear resistant properties as well as wrinkle and shrink resistance and are of high strength and possess a quality appearance. However, these polypropylene containing fabrics have, on the other hand, possessed the objectionable feature of having poor ironability. The ironability of a fabric is a very important property both to the producer and consumer. Fabrics which do not maintain their appearance or physical properties when ironed are not desirable and find little use in the manufacture of wearing apparel, curtains, bedspreads and the like. Thus, to be acceptable, a fiber and the fabrics prepared therefrom must retain their softness and appearance and at the same time be readily freed from wrinkles when ironed. Certain minimum ironing temperatures are necessary for successfully removing wrinkles from polypropylene containing fabrics. Such desirable ironing temperatures will vary depending on the particular fabric composition. Thus, for example, a pure polypropylene fabric will have a different ironing temperature than a fabric which consists of a blend of polypropylene and some other material. However, for polypropylene fabrics in general, where they are initially subjected to ironing temperatures which are apparently necessary for wrinkle removal, the fabrics become hard and shiny and the original qualities of the fabric cannot be recovered. Yet where lower ironing temperatures are used, wrinkles cannot be sufficiently removed from the fabrics. In fact, where the ironing temperature range is immediately below the temperatures at which the fabric becomes hard and shiny, crinkling of the fabric occurs. Where even lower ironing temperatures are used, there is practically no removal of wrinkles.

For example, when a new pure polypropylene fabric is ironed at temperature below about 100 C., wrinkles are not removed from the fabric. When ironed at temperatures between about 100 and about 119 C. the new fabric will crinkle if it is not subjected to tension or restraint. If the fabric is initially ironed at between about 120 and about 140 C., it becomes hard and shiny, which degradation is of a permanent nature and cannot be removed. Thus, it is evident that such a fabric may be easily ruined in an attempt to iron it. This same effect on other polypropylene containing fabrics is observed, with the Patented Sept. 23, 1969 temperature ranges differing depending on the type of blend and/or characteristics of the fabric.

It is an object of this invention to provide a process for improving the ironability of polypropylene containing fabrics. It is a further object to provide a process whereby a polypropylene containing fabric can be successfully ironed at a temperature suitable for removing wrinkles therefrom without causing the fabrics to become hard and/or shiny or otherwise deteriorated. These and other objects will become evident from the following description of the invention.

This invention provides a process for improving a polypropylene containing fabric which comprises heating the fabric at a sufficient temperature at which it will become crinkled if unrestrained or no tension is applied to the fabric but below the temperature at which the fabric becomes hard and/or shiny as compared to its original quality. By so heating the fabric, it can thereafter be easily ironed or otherwise heated without degradation at the higher temperature at which hardness and/or shine would have occurred had it not been initially heated at the lower temperature. Thus, the treated fabric can be successfully ironed at a higher temperature than is practical with the untreated fabric without crinkle of the fabric or without it becoming hard, shiny or otherwise deteriorated and with complete removal of wrinkles.

For example, a new pure polypropylene fabric when initially ironed at between about 120 and 140 C. becomes hard and shiny. This heating thus degrades the fabric significantly and further ironing at higher or lower temperatures does not restore the original qualities of the fabric. However, if when the fabric is first ironed at or otherwise heated to a temperature between about and 119 C., it may thereafter be ironed or heated to from about 120 to about C. without becoming hard or shiny or otherwise deteriorated. The initial heating (between about 100 and 119 C.) causes the fabric to crinkle somewhat if unrestrained or otherwise physically prevented from crinkling. However, this crinkle is thereafter easily removed by ironing at the higher temperature (about 120140 C.). Thus, by the initial heat treatment, the ironing temperature of the fabric is increased and the fabric itself becomes more resistant to future heat deterioration both as to its physical characteristics and appearance.

In a similar manner, fabrics consisting of blends of polypropylene and other materials such as polyethylene, acrylic and related acrylic copolymers (such as Orlon, Creslan, Acrilan, Darvan, Dynel, Zefran), vinylidene/ vinyl chloride copolymers, polyesters, polyamides (nylon), cellulose acetates, rayon, wool, cotton, silk, glass, etc., may be improved. Generally such fiber blends Will have a higher heating temperature at which crinkling and hardening and shine will occur as compared to pure polypropylene since the other fibers present may not be affected by heat at temperatures up to about C. as is the untreated polypropylene. Thus, for example, a fabric consisting of 50% polypropylene and 50% cotton must be heated to at least about C. and preferably at about -200 C. in order to remove wrinkles. However, in this temperature range, i.e., about 165 C. and above, the new fabric hardens and becomes shiny and even some melting of the fibers occurs. If the fabric is first heated at from about 150170 C., at which temperatures the unrestrained fabric merely crinkles, it can thereafter be ironed at temperatures up to 200 C. without hardening of the fabric and at which temperatures wrinkles and crinkles in the fabric are easily removed.

The propylene-containing fabric may be heated by any suitable means. It is preferable to use a means which allows for rather close control of the temperature being applied in order to prevent overheating. Heat may be applied by direct contact of the fabric itself with a heating unit such as a iron, etc., or the heat may be applied by the use of hot air, radiation, steam and the like. The heat should be as uniform as possible to avoid hot o cold spots on the fabric.

The length of time necessary for heating the fabric is dependent on the nature of the fabric itself as well as the temperature desired and heating means used. Heavier and thicker fabrics will require longer heating periods. In general, the length of time is not critical as long as the fabric is thoroughly heated at the desired temperature.

In some instances, it may be preferred to restrain the fabric in such a way as will prevent any slight crinkling or other shrinking while it is being initially heated. Although this restraint is not absolutely necessary it may be desirable especially where the heated fabric is to be directly processed for consumer use, etc., without further ironing. However, where a later ironing treatment or the like which will take out any crinkles or wrinkles is to be accomplished following the initial heat treatment or where a perfectly smooth fabric is not necessary or desired, the restraint of the fabric during the initial heating is not necessary.

Where it is advantageous or desirable to produce a fabric which is smooth without subsequent ironing, the fabric may be subjected to the initial heating while any crinkle or other surface shrinking is prevented. The particular means for preventing such surface irregularities is not critical. For example, any mechanical device may be used in which the fabric may be held in such a manner as will prevent its crinkling upon being heated. Thus, the fabric may be held in a frame type of device where the four edges of a sheet of fabric are held in place while the fabric is heated. Various types of apparatus may be used. Where a continuous process is used, a roll or bolt of fabric may be treated, for example, by heating the material as it passes on a roller or reel system, the fabric being held taut on the roller so that it does not become crinkled as it is heated.

The following examples are provided to illustrate the manner in which the invention is carried out. It is to be understood that the examples are for the purpose of illustration only and the invention is not to be regarded as limited thereby.

EXAMPLE I A pure polypropylene knitted fabric prepared from highly crystalline polypropylene fibers and having the dimensions 12" x 12" was ironed with a commercially available hand iron (General Electric, Model No. 71F81) heated to from about 100 to about 119 C. which was the lowest synthetic fabric setting. The fabric was ironed using normal iron pressures for about 1 minute. The fabric was somewhat crinkled but was hot hard or shiny or otherwise deteriorated from its original quality. Further ironing at that temperature did not completely remove the crinkles and wrinkles present.

The iron was then adjusted to the next higher synthetic fabric setting (about 120-140 C.) and the same fabric was ironed. There was no crinkling of the fabric nor did it become hard or shiny nor was its physical appearance altered in any way. Instead the fabric was easily ironed whereby all of the wrinkles and crinkles in the fabric were quickly removed. By comparison a substantailly identical fabric sample was ironed at about 120- 140 C. (second synthetic setting) without previous heating. The fabric became hard and shiny and badly crinkled and could not be returned to its original quality by further ironing at higher or lower temepratures.

EXAMPLE II A fabric sample containing pima cotton and 50% polypropylene fibers was hand ironed with the same iron 4 used in Example I at between about 150-170- C. The fabric became slightly crinkled. The fabric was then ironed at a higher temperature setting 175200 C. at which the crinkles were removed with the fabric retaining its original physical qualities and appearance. By comparison an identical fabric sample which was ironed at 175-200 C. without having been first heat treated at the lower temeprature became hardened and shiny with even some melting of fibers. Further ironing at higher and lower temperatures was ineffective in reducing the degradation.

EXAMPLE lII Untwisted polypropylene multifilament yarns of about 5 inches in length and 1000 total denier were laid over one another in a criss-cross pattern. The yarns were then ironed with the hand iron used in Example I for about 4-5 seconds with normal hand iron pressure. The samples withstood iron temperatures of -119 C. (lowest synthetic setting). Some samples withstood initial iron temperatures of l40 C. without drastic crinkles and fusion of the yarn fibers. However, all samples showed signs of fiber fusion when initially ironed at -160 C. (highest synthetic setting).

By comparison, untwisted polypropylene yarns were laid in a pattern as used above and placed in an oven at 140 C. for 3 minutes. These samples were then taken from the oven and cooled. When then ironed at 140- C. almost all yarns withstood the ironing without showing signs of melting or crinkle and all were improved.

We claim as our invention:

1. A method for preconditioning for ironing a polypropylene fabric stock material which becomes hard and shiny when ironed at an ironing temperature in the range from 120 to 140 C. which comprises (1) determining on a sample of said fabric stock a preconditioning temperature in the range between about 100 and 119 C. which is sufliciently high to cause said fabric, when heated thereto while unrestrained, to become crinkled but not hard and shiney, and

(2) heating said fabric stock to said preconditioning temperature, whereby said fabric stock is converted to a preconditioned fabric stock of improved ironability which can thereafter be ironed at said ironing temperature" without becoming hard and shiny.

2. A method for preconditioning for ironing a polypropylene-cotton blend fabric stock material which becomes hard and shiny when ironed at an ironing temperature in the range from to 200 C. which comprises:

(1) determining on a sample of said fabric stock a preconditioning temperature in the range between about 150 and C. which is sufficiently high to cause said fabric, when heated thereto while unrestrained, to become crinkled but not hard and shiny, and

(2) heating said fabric stock to said preconditioning temperature, whereby said fabric stock is converted to a preconditioned fabric stock of improved ironabilitywhich can thereafter be ironed at said ironing temperature without becoming hard and shiny.

3. A method for preconditioning for ironing a polypropylene-containing fabric stock material selected from the group of polypropylene fabrics and fabrics consisting of fiber blends of polypropylene with other textile fibers, which fabrics become hard and shiny when ironed at an ironing temperature in the range from 120 to 200 C., which comprises:

(1) determining on a sample of said fabric stock a preconditioning temperature in the range between about 100 and about 170 C. which is sufficiently high to cause said fabric, when heated thereto while 5 unrestrained, to become crinkled but not hard and shiny, and

(2) heating said fabric stock to said preconditioning temperature, whereby said fabric stock is converted to a preconditioned fabric stock of improved ironability which can thereafter be ironed at said ironing temperature without becoming hard and shiny.

4. The method according to claim 1 wherein said fabric is restrained against shrinkage during said heating step, whereby crinkling of the fabric is prevented during said heating step.

References Cited UNITED STATES PATENTS 2,440,209 4/1948 Redman 38144X 2,817,468 12/1957 Brown 38144 X 6 3,049,446 8/1962 Goldstein et al 38-144 X 3,051,674 8/1962 Kress 38144 X 3,323,190 6/1967 Boltniew 2872 OTHER REFERENCES Wall Street Journal article of Feb. 20, 1962 by R. A. Lewis; print enclosed.

l0 JORDAN FRANKLIN, Primary Examiner GEORGE V. LARKIN, Assistant Examiner US Cl. X.R. 

